Passiv

The house is being built.The car was completely destroyed.The mobile phone has been sold.

rules

What's the purpose of the passive voice?

You will find the passive voice mostly in written or formal spoken German e.g. news, reports on scientific experiments, newspaper, literature.
The passive voice is used to emphasise the action / process and not the agent (person or thing who is acting). It's not important who does something but what is done.

example:

active voice

passive voice

Herr Schmidt baut ein Haus. (Mr Schmidt is building a house.)

Ein Haus wird gebaut. (A house is being built.)

In the active voice the emphasis is placed on the agent (Herr Schmidt). It's important that he is the one who is building a house.
In the passive voice it doesn't matter who is building a house. The emphasis is placed on the action "ein Haus bauen".

How do you form the passive voice?

Präsens (present tense)

In the Präsens tense you form the passive voice with:form of "werden" + Partizip II

examples:

Ich werdegeküsst. (I'm being kissed.)

Du wirst verbannt. (You are being banned.)

Es wird verbrannt. (It is being burned.)

Wir werden verfolgt. (We are being followed.)

Ihr werdet entdeckt. (You are being discovered.)

Sie werden hergestellt. (They are being produced.)

Let's discuss the first example a bit more in detail.

active voice

passive voice

Cathy küsst mich. (Cathy kisses me.)

Ich werde geküsst. (I'm being kissed.)

"Cathy" is the subject in the active voice sentence. I'm the direct object and "kiss" is the verb.
In the passive voice the direct object turns into the subject and has, therefor, to be in the nominative case.
The verb is replaced by "werden" + Partizip II. The subject of the active voice sentence disapears usually completly.

How to state the agent?

Like in English there is a possibiliy to state the agent (=subject of the active voice sentence).
In English you use the preposition "by".

In German there are two prepositions to state the agent:

von (if the agent is a person)

durch (if the agent is an inanimate thing)

...whereby you will mostly need the von-agent.

examples:

passive voice without agent

passive voice with agent

Ich werde geküsst. (I'm being kissed.)

Das Haus wird zerstört. (The house is being destroyed.)

Ich werdevon Cathygeküsst. (I'm being kissed by Cathy.)

Das Haus wirddurch den Sturmzerstört. (The house is being destroyed by the storm.)

Passive voice in other tenses

Be aware that the passive voice is not a tense!The passive voice is a verb structure which allows you to emphasise the action/process
and this in every tense.

Präteritum (simple past)

In the Präteritum tense you form the passive voice with:form of "wurden" + Partizip II

examples:

Ich wurde verhaftet. (I was arrested.)

Die Stadt wurdezerstört. (The city was destroyed.)

Wir wurdengezwungen. (We were forced.)

Perfekt (present perfect)

In the Perfekt tense you form the passive voice with:form of "sein" + Partizip II + worden

examples:

Ich bin entlassenworden. (I have been released.)

Die Schule ist geschlossenworden. (The school has been closed.)

Die Probleme sind gelöstworden. (The problems have been solved.)

Plusquamperfekt (past perfect)

In the Perfekt tense you form the passive voice with:form of "war" + Partizip II + worden

examples:

Nachdem ich kontrolliertwordenwar, durfte ich in das Flugzeug. (After I had been checked I was allowed to enter the airplane.)

Als wir die Grenze erreichten, war diese bereits geschlossenworden. (When we arrived the border it had already been closed.)

Bevor der Forscher die Lösung fand, war das Problem bereits gelöstworden. (Before the researcher found the solution the problem already had been solved.)

Hint
What you learned so far about the passive voice should be enough on your current level.
However, I'd like add some more (complicate) theory for further studies.

Active sentences without a direct object

You learned that the direct object becomes the grammatical subject in a passive voice sentence.
What if there is no direct object included as you find in many dative sentences? Remember the indirect object is the dative case.

example 1:

active voice

Sie antwortet mir. (She answers me.)

"Sie" is the subject of the sentence

"antworten" is the verb of the sentence - a dative verb

"mir" is the indirect object

Since there is no direct object we use the dummy subject Es.

passive voice

Es wird mir geantwortet. (I'm being answered.)

"Es" is the dummy subject of the sentence

"wird" is the conjugated form of "werden"

"mir" is the indirect object

"geanwortet" is Partizip II of "antworten"

Now it becomes a bit crazy. It's logical to use a dummy subject if there is no subject
but it's even possible to leave out this dummy subject "Es" and keep the rest of the sentence.

Mir wirdgeantwortet. (I'm being answered.)

All we change is the word order of the remaining words
since the verb (here: helping verb "werden") has to be in the second position.

Be aware that "mir" is not the subject of the sentence.
"Mir" is obviously dative case and the subject is always in the nominative case.
The sentence doesn't contain a subject but we keep the conjugated form of "werden" as if
the dummy subject "Es" were there.

example 2:

active voice

Ich helfe den Kindern. (I help the children.)

"Ich" is the subject of the sentence

"helfen" is the verb of the sentence - a dative verb

"die Kinder" is the indirect object

passive voice (with dummy subject)

Es wird den Kindern geholfen. (The children are being helped.)

passive voice (without dummy subject)

Den Kindern wirdgeholfen. (The children is being helped.)

The following example makes this very clear:

Even if the dummy subject "Es" is not explicitly stated the verb "werden" has to be in the third person singular (wird).

Don't put "werden" because you think "die Kinder" is plural.
They are plural but they are not the subject of the sentence
and only the subject determines the conjugated form of "werden".

Active sentences without any object

There is no way in English to turn an active sentence without any object into a passive voice.
In German there is!